Marine exhaust valving

ABSTRACT

A marine engine exhaust system includes a catalyst arranged to intercept a flow of exhaust flowing along the exhaust system, a water muffler downstream of the catalyst, and a water-activated exhaust valve disposed between the water muffler and an upstream catalyst and configured to impede flow of water upstream from the muffler to the catalyst.

CLAIM OF PRIORITY

This application is a continuation of U.S. Ser. No. 10/974,380 filedOct. 27, 2004, and claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Patent Application Ser. No. 60/515,166, filed on Oct. 27,2003, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to marine exhaust systems.

BACKGROUND

Reducing combustion engine exhaust emissions is a continual object ofresearch and development, driven both by awareness of environmentaleffects and increased government regulation. Some of the most effectiveand cost-efficient emissions controls involve the use of downstreamchemical catalysts that further oxygenate incompletely combustedcompounds. Sometimes exhaust is directed sequentially through multiplecatalyst beds. It is generally understood that higher catalysttemperatures provide more effective emissions control.

Marine engines are subjected to specific regulations, both for emissionsand for safety concerns.

SUMMARY

According to one aspect of the invention, a marine engine exhaust systemincludes a catalyst arranged to intercept a flow of exhaust flowingalong the exhaust system, a water muffler downstream of the catalyst,and a water-activated exhaust valve disposed between the water mufflerand an upstream catalyst and configured to impede flow of water upstreamfrom the muffler to the catalyst.

In some embodiments, the catalyst is disposed downstream of an exhaustmanifold, such as a water-jacket manifold.

In some configurations the system also includes a water injection elbowdownstream of the catalyst, the injection elbow defining a water inletinto which water is injected into the flow of exhaust. In some cases theexhaust valve is disposed downstream of the injected elbow.

In some applications the exhaust system is mounted in a boat and furtherincludes an exhaust outlet at which the flow of exhaust is dispersedinto atmosphere outside the boat above a water line. In someembodiments, the exhaust passage extending from the water lift mufflerto the exhaust outlet extends to above the exhaust outlet, such as aU-bend.

The water lift muffler may include a drain.

In some embodiments, the system also includes a water level indicator,for example an indicator disposed between the water lift muffler and thecatalyst and responsive to rising water level to generate a warningsignal.

In some configurations the exhaust valve comprises a float valve, or aball valve having a ball floatable on a rising water level to close thevalve.

Preferably, the catalyst is configured to simultaneously reduce oxidesof nitrogen, carbon monoxide and hydrocarbons. The catalyst ispreferably configured to reduce carbon monoxide to between about 9 partsper million and 30 parts per million.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a marine engine-generator set.

FIG. 2 is a schematic cross-section illustrating flow through theexhaust manifold and elbow of the engine-generator set of FIG. 1.

FIG. 3 illustrates an alternative second exhaust manifold constructionand catalyst arrangement.

FIG. 4 is a perspective view of an engine exhaust manifold.

FIG. 5 is a partial cross-sectional view of the manifold of FIG. 4.

FIG. 6 shows a schematic view of a marine exhaust system according tothe invention.

FIG. 7 is a detail view of a float valve and water level indicatorcontained within the marine exhaust system.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring first to FIG. 1, an engine generator set 10 includes aninternal combustion engine 12 driving an electrical generator 14. Engine10 has an exhaust manifold 16 that receives and combines exhaust gassesfrom each cylinder of the engine and directs the combined exhaust gassesthrough a catalyst contained within the manifold, as discussed in moredetail below. Secured to the outlet of the manifold 16 is an exhaustelbow 18. In a marine application, water, such as cold seawater, issupplied to manifold 16 through hose 30. The water is directed throughcooling passages in manifold 16 and elbow 18 to keep the outer surfacesof the exhaust system at or below a desired temperature, and is theninjected into the exhaust stream in elbow 18, downstream of thecatalyst, to cool the exhaust.

In one embodiment, a variable is monitored with a feedback sensor 19located upstream of the catalyst which provides a control signal toelectronic controller 24. In one embodiment, controller 24 providescontrols the air fuel ratio of the engine 12 to correspond to a 1.0stoichiometric ratio. In other embodiments, the air fuel ratio of theengine 12 is slightly lean. In one embodiment, the variable monitored bythe feedback sensor 19 is oxygen and the feedback sensor 19 is anarrow-band oxygen sensor.

In one embodiment, an exhaust sensor 23 is mounted downstream of thecatalyst. In one embodiment, the exhaust sensor 23 measures oxygen as aproxy for indirectly determining the level of carbon monoxide. In thisapplication, a wide-band oxygen sensor can be used. In otherapplications, the exhaust sensor 23 directly measures carbon monoxide.The signal output from the exhaust sensor 23 can provide an anticipatoryalarm appraising an operator when the catalyst 32 is functioning withreduced effectiveness. Accordingly, the exhaust sensor can inform theoperator if the catalyst 32 has been damaged by seawater and requiresreplacement. The exhaust sensor 23 can be a MEMS device in someembodiments.

With continued reference to FIG. 1 and in an alternative embodiment, airis delivered to manifold 16, through a controllable dump valve 20, frombelt-driven air pump 22. A fixed speed, electric air pump may also beemployed. Valve 20 is controlled by an electronic controller 24 tomoderate the flow of air into manifold 16 as a function of the loadplaced on engine 12, such as by controllably dividing the output of theair pump between manifold 16 and exhaust elbow 18. Controller 24 variesa signal to valve 20 as a function of engine load, or as a function of asensible parameter that changes with engine load. In the illustratedembodiment, controller 24 senses an output voltage and/or current ofgenerator 14, such as at generator output 26, and controls valve 20accordingly. Controller 24 also senses engine speed, such as byreceiving a signal from flywheel magnetic reluctance sensor 28, andcontrols engine inputs (such as fuel and/or air flow) to maintain enginespeed at or near a desired set point, so as to maintain the frequency ofgenerator 14. As an alternative to controlling a dump valve 20 splittingpump air flow between manifold 16 and either atmosphere or a lower pointin the exhaust stream, a variable speed electric air pump 22 a isemployed in some instances, with controller 24 varying the operatingspeed of pump 22 a as a function of engine load. In such cases, theentire output of pump 22 a is preferably ported directly to manifold 16.

Referring to now FIG. 2, a cylindrical catalyst 32 containing a catalystbed is shown disposed within the exhaust manifold 16. The catalyst 32 iswrapped in an insulating blanket 96, such as a ⅛ (3.2) millimeter thicksheet of cotton binding containing mica, for example, that helps reduceheat transfer from the catalyst into the housing and also helps toisolate the delicate catalyst bed from shocks and vibrations. In oneembodiment, controlled air flow is injected either just forward of thecatalyst at port 38 a, or at the far end of the manifold at port 38 b soas to preheat the injected air flow. Single catalyst 32 may be of anypreferred composition, such as a palladium-platinum catalyst, forexample. In other embodiments, no air flow injection is required.

With continued reference to FIG. 2 and in one embodiment, catalyst 32 isconfigured and dimensioned for fitting within a marine exhaust manifold16. In one presently preferred embodiment, the catalyst 32 has adiameter of 3.66 inch (9.30 cm) and a length of 6.0 inch (15.24 cm ).The catalyst 32 can include a round ceramic having a diameter of 3.0inch (7.62 cm) and a length of 6.0 inch (15.24 cm) and a 400-cells perinch with 95-grams per cubic foot of a 3-to-1 of platinum to rhodium.The catalyst 32 can also include a specialized wash coat designed to bethe most effective at a 1.0 stoichiometric air fuel ratio. The catalyst32 is configured to simultaneously reduce oxides of nitrogen, carbonmonoxide and hydrocarbons. In one preferred embodiment, the catalyst 32is configured to reduce carbon monoxides levels to below 50 part permillion, preferably to below 35 parts per million, and most preferablyto below ambient levels, i.e., 9 part per million.

Other catalyst configurations are contemplated within the exhaustmanifold 16. For example as illustrated in FIG. 3, the catalyst 32 in analternative embodiment can include a first catalyst 33 and secondcatalyst 36 contained within a second bore of the manifold, parallel toand offset from the first bore. The manifold can be equipped with aremovable cover 44 through which the air is injected, enabling loadingof both of the catalysts into their respective bores. As in the firstillustrated embodiment, after flowing through both catalyst beds theexhaust flow is combined with cooling water in elbow 18 a.

The exhaust is combined and directed through a first catalyst bed 32,through a space 34, and then through a second catalyst bed 36. The airis injected into the manifold in space 34, through air inlet 38. Coolingwater flows around both catalyst beds, through appropriate channels castinto manifold 16 a and elbow 18, and is then injected into the exhaustflow. In marine applications where the cooling seawater can have a highsalt content, the water injection outlets 40 in elbow 18 are preferablyat least about six inches (15 centimeters) below the lowest edge of thecatalysts or the upper edge of any internal elbow baffles 42 positionedto avoid salt water splash on the hot catalysts. Also, it is preferredthat for such marine applications manifold 16 a and elbow 18 be cast ofa corrosion-resistant material, such as an aluminum-magnesium alloy. Itwill be apparent from FIG. 2 that the connection between manifold 16 aand elbow 18 can be readily positioned between the two catalyst beds,such that second catalyst 36 is carried within elbow 18.

The construction of the catalyst 32 according to this embodiment caninclude a first catalyst bed 33 which preferably includes a catalystsuch as one containing rhodium as the precious metal, selected to reducehydrocarbon and NO_(x) emissions. For example, one preferred catalystbed is in the form of a cylinder 3.0 inches (76 millimeters) in diameterand 2.6 inches (6.7 centimeters) long. The ceramic substrate has across-sectional area of about 7 square inches (45 square centimeters)and has about 400 cells per square inch (62 per square centimeter), andis washed with 6.1 grams per cubic foot (0.06 grams per cubiccentimeter) of rhodium. Such a catalyst bed is available fromASEC/Delphi Exhaust and Engine Management of Flint, Mich. Catalysisefficiency within first catalysis bed 33 may be accomplished by variousmethods known in the art, either in carbureted or fuel-injected systemswith oxygen sensors, to remove as much of the overall emissionscomponents as possible.

The second catalyst bed 36 contains a catalyst selected to furtherreduce CO emissions. In one arrangement, second catalyst bed 36 containsa three to one ratio of palladium and platinum, carried on ahoney-combed substrate of ceramic or metal. The active precious metalsare washed onto the substrate and then heated to set the metals onto thesurface as known in the art. An example of a preferred second catalystbed is a metal substrate in the form of a cylinder of 5.0 inch (12.7centimeter) diameter and 6.3 inch (16 centimeter) length, with 19.6square inches (126 square centimeters) of cross-sectional area, washedwith 40 grams per cubic foot (0.4 grams per cubic centimeter) each ofpalladium and platinum. Such a catalyst is available from Miratech ofTulsa, Okla., for example. Second catalyst 36 will tend to run hotter,such as perhaps about 400 degrees Fahrenheit (220 degrees Celsius)hotter than the rhodium catalyst. Preferably, the temperature of thecombined air and exhaust entering the second catalyst is about 1000degrees Fahrenheit (540 degrees Celsius).

FIGS. 4 and 5 show another example of a catalyst exhaust manifold 16 b.The catalyst 32 is loaded as a cylinder from the large end of themanifold, with the NO_(x) catalyst loaded into bore 46. (FIG. 5) and theCO catalyst loaded into bore 48 (FIG. 5). In this example, coolantenters the manifold at inlet 50 and leaves the manifold at outlet 52,without joining the exhaust stream. The cooling channels 54 cast intothe manifold are partially shown in FIG. 5, providing a closed flow pathbetween inlet 50 and outlet 52.

Various control techniques may be employed to vary air injection ratefor good CO reduction. In one embodiment, the air injection rate isvaried as a function of approximate engine load. In one test using aWesterbeke 4-cylinder, 1.5 liter gasoline engine and thepalladium-platinum second catalyst bed described above, the lowest COemissions were provided by varying the rate of air flow into themanifold ahead of the second catalyst (a 100 liter per minutegraduations) according to the following table; Engine Load Air Flow Rate(Percent Full Load) (liters per minute) 100 500 75 500 50 500 25 400 10300 0 300

Of course, optimal air flow rates will be different for differentapplications. The air flow controller can be configured to interpolatebetween adjacent entries in the load-air correlation table to providefiner control sensitivity.

There are various ways to determine approximate engine load, such that atable like that shown above can be used to determine an optimal airinjection rate. For example, if substantially all of the engine load isprovided by an electrical generator (as shown in FIG. 1), monitoring theelectrical output of the generator can provide a good estimate of engineload. Current can be monitored as a most direct measure of electricalload, such as by providing a current transformer about the output of thegenerator. In some cases in which generator voltage is known topredictably decrease a measurable amount with load, voltage mayalternately be monitored. In most cases, however, current monitoring ispreferred for systems with proper generator voltage regulation. Otheroptions include measuring engine output driveshaft torque (or somemeasurable parameter that varies predictably with torque), or measuringthe pressure within the manifold, such as upstream of the catalyst beds,or exhaust backpressure below the catalysts and above a muffler or otherexhaust restriction. Because the engine speed is substantially fixed inthe primary embodiments, other parameters may also be found to varypredictably with engine load, such as throttle position and fuel flowrate, for example.

As a alternative to controlling the air injection rate as a function ofload, the air injection rate can be controlled as a function of othermeasured parameters that signify catalysis efficiency. For example, a COsensor may be provided downstream of the catalyst as described above.

With renewed reference to FIG. 2 an in one embodiment, an exhaustpressure sensor 62 can be placed in the manifold 16, to measure exhaustmanifold pressure, or downstream of the catalyst 32 to measure exhaustbackpressure developed upstream of a muffler or other exhaustrestriction (not shown). If the air pump delivering air to inlet 38 isnot a fixed displacement pump, changes in exhaust backpressure withengine load can cause a significant fluctuation in the injected airrate. This fluctuation will tend to work against the desired variationof air flow rate with engine load, as backpressure, which rises withengine load, will cause a reduction in air injection rate that should beaccounted for in the control of the pump or valve. It will be understoodthat sensors 62 are shown in optional and alternative locations, and arenot necessary in some embodiments, such as when air flow rate iscontrolled as a function of generator current or some other primarycontrol parameter.

Referring now to FIG. 6, an exhaust system 60 for the engine 12 mountedin a boat 67 is shown. The exhaust manifold 16 directs exhaust gasesthrough the catalyst 32 and exhaust elbow 18 and past a water injectedexhaust elbow 65. To reduce the operating temperature of the exhaustcomponents, cooling seawater is injected at the inlet to the exhaustelbow 70. The exhaust gases and cooling water then pass through anexhaust valve and water level indicator 75 (discussed in more detailbelow). The exhaust gasses and cooling water enter a water lift marinemuffler 80 before proceeding to a high point at the U-bend 85 and out ofthe boat through the through-hull fitting 90 above the water line 97. Inone embodiment, the muffler 80 includes a drain 97.

In marine applications, it is desirable to prevent cooling seawater fromcontacting the catalyst 32 disposed within the exhaust manifold 16. Itis also desirable to prevent cooling seawater from reaching the engine12, which can result in catastrophic failure. Referring to FIG. 7 anexhaust valve and water level indicator 75 are shown and disposed withinthe marine exhaust manifold 16 between the water injected exhaust elbow65 and the water lift muffler 80 (FIG. 6). The valve/indicator 75 caninclude a float valve 105, such as a ball valve and a water levelindicator 110 combined in a housing 115. The ball valve 105 translatesalong the housing 115 between ball valve guides 120 a, 120 b and issupported by ball valve supports 130 a, 130 b when the ball valve isdisposed in an open position 135 (shown in phantom ). When the ballvalve 105 ascends upward to the closed position (as shown) the surfaceof the ball valve 105 contacts the housing 115 along valve sealing areas140 a, 140 b thereby closing the valve. The rising water level withinthe housing 115 floats the water level indicator 110 upward to an alarmlevel which provides a signal 145 to warn an operator that the muffler80 is overfilled.

A number of embodiments of the invention have been described. Forexample, the engine 12 as described above can be used for propulsion inmarine applications. Nevertheless, it will be understood that variousmodifications may be made without departing from the spirit and scope ofthe invention. Accordingly, other embodiments are within the scope ofthe following claims.

1. A marine engine exhaust system comprising: a catalyst arranged tointercept a flow of exhaust flowing along the exhaust system; a watermuffler downstream of the catalyst; and a water-activated exhaust valvedisposed between the water muffler and an upstream catalyst andconfigured to impede flow of water upstream from the muffler to thecatalyst.
 2. The exhaust system of claim 1 further comprising an exhaustmanifold, and wherein the catalyst is disposed downstream of the exhaustmanifold.
 3. The exhaust system of claim 2, wherein the exhaust manifoldis water-jacketed.
 4. The exhaust system of claim 1 further comprising awater injection elbow downstream of the catalyst, the injection systemdefining a water inlet into which water is injected into the flow ofexhaust.
 5. The exhaust system of claim 4, wherein the exhaust valve isdisposed downstream of the injection elbow.
 6. The exhaust system ofclaim 1 mounted in a boat and further comprising an exhaust outlet atwhich the flow of exhaust is dispersed into atmosphere outside the boatabove a water line.
 7. The exhaust system of claim 6, including anexhaust passage extending from the water lift muffler to the exhaustoutlet and extending above the exhaust outlet.
 8. The exhaust system ofclaim 1, wherein the water lift muffler includes a drain.
 9. The exhaustsystem of claim 1 further comprising a water level indicator.
 10. Theexhaust system of claim 9, wherein the water level indicator is disposedbetween the water lift muffler and the catalyst and is responsive torising water level to generate a warning signal.
 11. The exhaust systemof claim 1, wherein the exhaust valve comprises a float valve.
 12. Theexhaust system of claim 1, wherein the exhaust valve comprises a ballvalve having a ball floatable on a rising water level to close thevalve.
 13. The exhaust system of claim 1, wherein the catalyst isconfigured to simultaneously reduce oxides of nitrogen, carbon monoxideand hydrocarbons.
 14. The exhaust system of claim 1, wherein thecatalyst is configured to reduce carbon monoxide to between about 9parts per million and 30 parts per million.